100 Watt Hi-Fi MOSFET Power Amplifier Circuit

This power amplifier uses MOSFET IRFP240 and IRFP9240 as displayed in the circuit. This amplifier operates at +45 / -45 VDC and can provide 100 Watt RMS output on an 8-ohm loudspeaker. If the speaker is changed to 4 ohms, the power output will be 160 Watt RMS.

The use of this amplifier is very much, among others, as a guitar amplifier, amplifier keyboard, or for home studios. This amplifier can also be made as a subwoofer amplifier but you must add a complete subwoofer circuit module.

This amplifier is very suitable to be used as a universal Hi-Fi amplifier because it has a very low distortion level, which is 0.1% with an input sensitivity of 1.2V. Besides this amplifier also has a wide bandwidth between 4Hz to 4kHz.

mosfet power amplifier

How the circuit works

C2 is a capacitor that functions to block the DC voltage at the amplifier input. This capacitor is very important so as not to change the bias at the base of the transistor Q1. While resistor R2 serves to flow input to transistor Q1 through capacitor C1. Capacitor C1 will reduce noise at the input.

Potentiometer trimmer. Usually, a variable resistor is designed so that the output gets 0V when the input is standby. Resistors R10 and R11 will determine the amplification value of the amplifier. Transistors Q1 and Q4 are differential amplifiers.

The second differential amplifier circuit is built by transistors Q5 and Q6, while transistors Q7 and Q8 will make a current mirror so that the second differential amplifier (Q5 and Q6) can flow the connected current. This is done to produce a linear output.

The amplifier is built by MOSFET IRFP240 and IRFP9240 which are operated in class AB. Class AB will produce efficiency of around 78%. Network capacitors C8 and R1 are used to increase high frequencies and prevent increased oscillations.

In the voltage supply section, you will see a 3A fuse as a safety so that the power supply is safe in the event of a short circuit.

Circuit Setup before used.

So that the amplifier can be used properly, you must first setup it before using it. Set resistor R1 to the center point before the circuit is ON. Then turn on the amplifier and set the output R1 to 0 Volts. After that set R16 so that points X and Y get 16.5 mV

To avoid noise and interference, making this amplifier must use a good quality PCB. Then use the CT 3A power supply transformer, and the power supply must not exceed +/- 55 Volts because it will be damaged in series. Before connecting to the loudspeaker, first, measure the speaker output voltage should not exceed 50mV, if when exceeding 50mV excess, check the circuit may be an error.

Or another problem replacing transistors Q1 and Q4 can solve the problem. The final transistor needs a heatsink to keep the temperature safe while the circuit is maximum operated. Also, use all metal film resistors on all components.

Power supply for 100W MOSFET power amplifier.

power supply for amplifier

In general, a 100 Watt power amplifier MOSFET circuit can use any power supply as long as it complies with the provisions (35 VAC CT and 3A). But it is advantageous to use a 6 A bridge diode because it will be stronger. But if not, you can replace it with four 6A diodes. The capacitor power supply should not be less than 10000 uF because the capacitor filter will not work perfectly.